This invention relates to inertial-type engine air particle separators for turbine engines, particularly turbine engines for aircraft.
Over the past decade the Army has lost millions of dollars as a result of foreign object damage to turbine engines. In fact sand and dust erosion is one of the major problems facing Army aviation and other users of gas turbine engines. The best known example of damage is erosion of both leading and trailing edges of compressor blades due to sand and dust ingestion. In addition since particles traveling from stage to stage are centrifuged outwardly, they also erode the compressor housing and stator vanes. Compressor erosion has presented a problem to both airframe and engine manufacturers.
The need to protect turboshaft engines from foreign object ingestion became especially apparent in Southeast Asia. Virtually all military helicopters had to be provided with engine air particle separators.
The high demand for engine erosion prevention has led to the development of four types of particle separators: barrier filters, single tube inertial separators, multi-tube inertial separators and two stage separators utilizing combinations of inertial separators.
Filters have been used on several helicopter models. However, high maintenance requirements, and the high pressure drops when filters are loaded with sand are disadvantageous. In addition failures result from filters becoming clogged or collapsed.
Inertial-type particle separators are generally categorized according to flow. Flow paths in these separators are either axial or radial. Such separators are shown in FIGS. 1 and 2. One type of axial flow separator consists of an array of small vortex tubes, such as that shown in FIG. 1, mounted in parallel in a tube sheet 2. Dirt particles in the air are swirled to the outer walls 4 of a vortex tube by vortex generator 6. Scavenge air carrying the contaminants flows out passageway 8 and the clean air enters the engine through outlet tube 10. Such tubes are generally about 1 1/2 inches in diameter and two to four inches long.
The particle separator shown in FIG. 2 is also an axial flow device, consisting of an inner annulus 12, a stage of swirl vanes 14, a stage of scroll vanes 16, a collection or scavenge scroll 18 and a stage of exit deswirl vanes 17 which are in front of the engine compressor inlet. Inlet swirl vanes 14 impart a rotational velocity to the inflowing air, thereby generating a vortex flow field. Owing to their greater inertia, foreign particles caught within this flow field are centrifuged to the outer wall 19 of the separator. These particles are then drawn into the scavenge scroll 18 and finally bled off through a scavenge outlet along with a small percentage of excess air. The remaining air passes through the exit deswirl, or straightening, vanes 17 which remove any residual swirl at the exit of the separator to deliver clean, undistorted air to the engine compressor. An auxiliary fan can be used to supply a scavenge suction source, an alternate but less efficient scavenge suction source being an ejector system.
A combination particle separator is shown in FIG. 3. Such powered centrifuged separators are deemed to meet future fine particle performance requirements. Such a powered separator, typically utilizing a centrifugal impeller or a rotating member 20, can centrifuge particles to the periphery of the flow field by imparting a whirl component to the air flow which in turn imparts this motion to the particles. Because the centrifugal force on a rotating particle increases with the distance of the particle from the center of rotation, it is advisable that the fine-particle-laden airstream enter a powered centrifugal separator around a center body 22 so that particles are already well out on a radius as they enter. The center body 22 is employed as a conventional inertial separator, as shown in FIG. 3 affording a further advantage.
There is provided herein a scroll or radial separator having no swirl vanes, no scroll scavenge vanes, no deswirl vanes and the air intake can be readily adopted for the introduction of air from any direction. All incoming air to the engine must pass through the scroll separator before it can enter the engine. Since great flexibility of design is possible the separator is adoptable to a variety different installation configurations.